The present invention relates to method and unit for processing a contaminated liquid, and more particularly relates to formation of a field of super critical conditions within an agitation chamber containing a liquid contaminated with a harmful compound or compounds such as polychlorinated biphenyl (PCB) unsuited for any chemical reactions under normal conditions for the purpose of liberation and removal of such a compound or compounds.
In this specification, the term xe2x80x9ca harmful compoundxe2x80x9d refers to a compound which poses malign influences, in any forms, on healthy human life and is unsuited for any chemical reactions under normal conditions.
Further, the term xe2x80x9cperforatedxe2x80x9d encompasses a substantially planar construction which is provided with one or more holes opening in both surfaces of an agitator and/or one or more recesses formed in at least one of both surfaces of an agitator.
Conventionally, the following expedients have been generally employed in order to convert a harmful compound, which is unsuited for chemical reactions by use of reactants under normal conditions, into a harmless compound via reactions.
One of such expedients is called xe2x80x9cseparation of super critical water by oxidationxe2x80x9d. Here the term xe2x80x9csuper critical waterxe2x80x9d refers to a kind of water placed under a condition in which the temperature is 374xc2x0 C. or higher and the pressure exceeds 22 MPa. Such a water has a property to move actively just like gases to separate a target, i.e. a harmful compound. In practice it is required that the temperature is about 600xc2x0 C. and the pressure is about 22 MPa.
Another of such expedients is called xe2x80x9cseparation by alkali catalystxe2x80x9d. In the case of this process, hydrogen provider, carbon type catalyst and alkali such as potassium hydroxide are added to a harmful compound, and the mixture is heated at a temperature in a range from 300 to 350xc2x0 C. under presence of nitrogen in order to eliminate a part of the harmful compound, for example chlorine in the case of PCB.
In the case of such conventional expedients, however, it is necessary to carry out the process within a closed environment under high temperature and high-pressure conditions and/or under presence of nitrogen gas. This entails use of a reaction device well resistant to corrosions by high temperature, high pressure and reaction gas. In addition, high level of process control and maintenance of the device are required. For these reasons, the conventional expedients are suited for only batch-type processing but not for continuous processing. Consequently, all of the conventional expedients were not feasible in practice from the viewpoint of economic efficiency.
It is thus the primary object of the present invention to enable rapid conversion of a harmful compound into a harmless compound such as dechlorination of PCB under normal temperatures and normal pressures in a continuous mode.
In accordance with one aspect of the present invention, an agitation chamber is provided which incorporates two or more horizontal perforated agitators arranged in a vertically spaced superposed positions, a mixed solution of contaminated liquid containing harmful compounds and reactant capable of coupling to free radicals from the compounds is prepared, the mixed solution is charged into the agitation chamber, the agitators are driven for rotation at a speed in a range from 10,000 to 18,000 rpm, and a processed solution is discharged from the agitation chamber.
In accordance with another aspect of the present invention, a vertical-type agitation chamber is formed in a substantially closed construction, two or more horizontal perforated agitators are incorporated in the agitation chamber in a vertically spaced superposed arrangement, means are provided for charging into the agitation chamber a mixed solution of a contaminated liquid containing harmful compounds and a reactant capable of coupling to free radicals from the compounds, means are provided for driving the agitators for rotation at a speed in a range from 10,000 to 18,000 rpm, and means are provided for discharging a processed solution from the agitation chamber.
The agitator may take the form of either a circular disc or a branched disc.
In the system of the present invention of the above-described aspects, high-speed rotation of the agitators causes intense and dynamic frictional contact of the mixed solution with the surfaces of the agitators. This frictional contact generates heat of high temperature (from 230 to 300xc2x0 C.). In addition, centrifugal force caused by the frictional contact strongly compresses the mixed solution within the holes and/or recesses in the agitators and the mixed solution in the region near the side wall of the agitation chamber, thereby creating a high pressure condition of 22 MPa or higher. Further, due to Bernoulli effect, high speed rotation of the agitators causes a large pressure drop in the mixed solution and such pressure drop causes generation of lots of fine bubbles via cavitation. These fine bubbles are destroyed by shearing force created by the high-speed rotation of the agitators.
Combination of the high temperature with the high pressure creates a field of super critical conditions within the agitation chamber. Such conditions induce a radical reaction by which a part of the contaminated liquid is liberated in the form of free radicals. In addition, destruction of the fine bubbles generates super sonic which promotes the above-described radical reaction.